Anemometers are primarily used to measure air flow and commonly comprise a rotating element whose angular speed of rotation is correlated with the linear velocity of the air flow. Cup and vane anemometers are by far the most prevalent. The cups typically spread over 120 degree angles, attached at a central hub. The center of the hub translates rotational movement along a vertical axis when the cups respond to air movement in the horizontal plane. The rotational movement relates to the speed of the impinging air currents and thus to wind speed. One of the drawbacks of this type of anemometer is that the inertia of the mechanical mechanism must be overcome. The weather vane device requires a very free gimbal so as to allow the device to point accurately into the wind at very low wind speeds. As a result of its reliance on this mechanical element, the anemometer is not conducive to measuring gusts, and is subject to errors in measurement due to overshoot, oscillations that occur due to change in wind direction, and wind measurement even when the wind is not blowing.
Still another type, a sonic anemometer uses sound waves to measure wind direction and speed. These are a class of instruments that are typically used by research and other scientific organizations. These systems use the changes in the speed of sound as measure over a finite path. Whilst these instruments overcome the failings of the more prevalent cup and vane they cost considerably more to purchase and maintain. Also, the sonic devices tend to be very power hungry, so although suitable for unattended operation, considerable cost and compensatory mechanisms must be built into the device for continuous remote operation.
Other force sensing vertical rod type anemometers are known. In one example Shoemaker (U.S. Pat. No. 7,117,735) uses a simple, single pickup wind drag force measurement system. Therefore, although addressing the cost threshold, the accuracy of measurement is modest. Moreover, the device is sensitive to inclinations of the base, and has no built in device as a compensatory mechanism for correcting the inaccuracies that would result.
Another vertical shaft sensor design, Gerardi (U.S. Pat. No. 5,117,687) uses a sphere attached to a shaft. When the wind force moves the shaft, electromagnetic or optical sensors detect the deflection from the neutral position. The air data sensor uses a relative difference method to measure deflection using four orthogonally placed sensors in addition to two more sensors for complete 3-axis velocity measurements. One drawback to this design is the excessive use of strain gauges contributing to the overall complexity of the design. Moreover, this invention requires a counterweight to function in an inclination independent manner.
Portable wind sensors typically involve a weather vane structure that points a fan-based anemometer in the direction of the wind to measure wind speed. Other types require the operator to point a fan-based anemometer into the wind. These are generally unsuitable for unattended operation, suffering from inaccuracies in measurement and are generally less sensitive than more expensive designs.